1. Field of the Invention
This invention relates to the construction and operation of lasers capable of operating at a very high excitation power levels and very high excitation frequencies, in the order of 200 megahertz to 10 gigahertz. The invention provides for operation at gas pressures in excess of one atmosphere, and for excitation levels exceeding 10 kilowatts per cubic centimeter.
2. Description of the Prior Art
In much of the prior art lasers, low pressure carbon dioxide has been utilized as the lasing gas, and low excitation frequencies in the order of ten to two hundred megahertz have been used. However, there have a limited number of reports of use of higher excitation frequencies and other lasing gases:
An X-Band RF pumped laser which operates in the frequency range of 8 to 12 gigahertz has been developed by Waynant, Epp, and Christensen U.S. Pat. No. 4,513,414. In this device, RF (radio frequency) coupling to the lasing medium is provided by a coupling plate forming a common wall between a wave guide and a RF cavity. A standing wave pattern is produced within the RF cavity which excites a lasing medium. Since these devices use a hollow wave guide coupling structure, they become extremely large and cumbersome at lower frequencies. In this design preionization is accomplished by use of an auxiliary discharge tube.
RF excitation of an XeF laser with a 200 megahertz source has been reported in an article entitled "200 MhZ Eelectrodeless Discharge Excitation of an XeF Laser", by Christensen and Waynant, Applied Physics Letter 41(9), p. 794, Nov. 1, 1982. In this device the physical size of the laser was small enough to allow lumped circuit techniques to be used in its design. However, no preionization was used, and the design was suitable for use with RF frequencies of no more than a few hundred megahertz.
Lasers excited by RF discharges produced in tapered sections of hollow wave guides are also known and have been described in the U.S. Pat. No. 4,004,249, Kikuchi; and in an article entitled, "LASER Generations by Pulsed 2,45-GH.sub.z Microwave Excitation of CO.sub.2 ", by Handy and Brandelik, Jour. Appl. Phys. 49(7), p. 3753 (1978). These devices utilize hollow wave guide structures and hence become extremely cumbersome at frequencies below 2 gigahertz. In these devices there has also been no disclosure of any preionization, and there is no disclosed use of high pressure gases. This apparatus essentially consists of placement of a pyrex lasing tube parallel to the H plane of a rectangular S-band wave guide.
Capacatively ballasted lasers using lower RF frequencies are known. These lasers operate at frequencies in the 30 megahertz range and utilize lumped circuit techniques for construction of the discharge head and for impedance matching. These devices however are not useful at high RF frequencies where transmission line techniques must be employed.
An unballasted RF discharge laser has been described in a patent awarded to Laakmann, U.S. Pat. No. 4,169,251. This unballasted configuration has been used in commercial carbon dioxide lasers marketed by Laakmann Electro-optics and by Hughes in the United States. These devices however operate at gas pressures below one atmosphere and at relatively low excitation levels. At higher gas pressures and high RF power levels, unballasted RF discharges develope inhomogeneities and instabilities that severly limit their utility. Still further, the use of metallic electrodes in contact with the laser gas is undesirable when corrosive gas mixtures are considered.